In the various kinds of industrial fields, generally, waste water is discharged in a considerable abundance. The treatment process of the waste water creates inevitably a considerable amount of the sludge which contains water. When the contained water is extracted from the sludge, it becomes so called "sludge cake". It is preferable that the amount of contained water of sludge cake could be reduced as low as possible in order to deal with it easily after fact.
In a sludge filtration apparatus of the prior art, 2 sheets of filtering fabrics or nets are arranged on the low and high portions of the main frame respectively. And the filtering fabrics or nets move along around plural number of rollers under tension produced by a pair of rollers in order to dehydrate the sludge.
In such a sludge filtration apparatus of the prior art, there are several problems as followings
First, the filtering fabrics or nets tend to be always and seriously contaminated by particles of sludge. Ilence, timely, they have to be washed with enormous amount of water.
Second, since the filtering fabrics or nets are tensioned to dehydrate the sludge, they are continuously and excessively stretched and rubbed against the rollers by tension and turning force of rollers. As a result, the fabrics or nets tend to be worn out and damaged in relatively earlier stage to shorten lifetime thereof.
Third, in the prior art, frequent trouble of the run-off-the-track preventing device causes the filtering fabrics or nets to be broken down, and tends to halt the dehydrating process of sludge repeatedly for a short time or a long time occasionally.
Fourth, the sludge filtration apparatus of the prior art has a complicated structure which includes driving devices, tension controlling devices, washing devices, run-off-the-track preventing devices and so forth. Therefore, so many operators should check and maintenance the equipments continuously and frequently to spend large labor time in managing the large and complex facilities hardly. Also, frequent checking and maintenances require the casings of the equipments to be often opened, so that the opened equipments discharge contaminated airs which makes bad smell and air pollution unavoidable in the factory environments.
Fifth, in order to reduce the amount of the contained water of sludge cake rapidly and effectively, it would be preferable that sludge on the filtering fabrics or nets can be pressed between a pair of roller (pressing technique) or be sucked by suction device (sucking technique). In the above prior art, however, both such a pressing technique and sucking technique could not be available to the apparatus because these techniques cause sludge as well as water to pass the fabrics or nets, and cause the fabrics or nets to be clogged by the dust or dirt lumps and to be useless rapidly. So, in the prior art, in order to dehydrate sludge, areas of meshes in the filtering fabrics or nets should be widen only by applying the tension to the fabrics or nets (tension technique). But in the tension technique of prior art, workability is relatively low, and it requires many times in processing. And the resulted sludge cake of the above prior art has relatively higher amount of contained water.
In order to solve the problems of the prior art mentioned above, the 30 applicant of this invention filed Korean Utility Model No. 1997-18821 which discloses a sludge filtration apparatus including pressing rollers and a filtering belt. The filtering belt of '1997-18821 has plural of filtering units with chemical resistant fine fibers of synthetic resin joined thereon, and a thick rubber belt on which plural of through-holes for passing sludge water are formed and to which the filtering units are attached one after another along the longitudinal direction of the rubber belt.
In the sludge filtration apparatus of '18821, in first, water of sludge is absorbed on the fine fibers of synthetic resin of the filtering units. Then the sludge and filtering units are pressed between a pair of rollers to extract water from them to yield to the sludge cake. So, the resulted sludge cake of the '18821 can has less amount of contained water than the above prior art's.
In the '18821, however, there are also some problems as followings
First, in the apparatus of '18821, the filtering units are attached to the rubber belt in a manner that the rubber belt has a flexible rod fixed on the bottom thereof and the filtering units are tied up to the flexible rod by a metal wire. When the filtering units are worn out or damaged and have to be replaced with new ones, operator should untie the old one from the rod and then again tie new one up manually. Therefore, so much time and labors should be required in the replacement work.
Second, in the apparatus of '18821, since only the rollers are involved in pressing sludge on the filtering unit, there is a limit to reducing the amount of contained water of the resulted sludge cake.